Conventionally, an electric resistance-type PM sensor has been known as a sensor which detects PM in exhaust gas discharged from an internal combustion engine. In a general electric resistance-type PM sensor, a pair of conductive electrodes are disposed in a face-to-face fashion on a surface of an insulated substrate, so that a PM amount is estimated by making use of the fact that an electric resistance value changes due to conductive PM (mainly, a soot component) adhering to these electrodes (for example, refer to Patent Literature 1).